298 CAUSATION 



which has served us well in the past. Indeed it is a 

 healthy attitude to assume that nothing is beyond the 

 scope of scientific prediction until the limits of prediction 

 actually declare themselves. 



(2) The current epistemology of science presupposes 

 a deterministic scheme of this type. To modify it in- 

 volves a much deeper change in our attitude to natural 

 knowledge than the mere abandonment of an untenable 

 hypothesis. 



In explanation of the second point we must recall 

 that knowledge of the physical world has to be inferred 

 from the nerve-messages which reach our brains, and 

 the current epistemology assumes that there exists a 

 determinate scheme of inference (lying before us 

 as an ideal and gradually being unravelled). But, as has 

 already been pointed out, the chains of inference are 

 simply the converse of the chains of physical causality 

 by which distant events are connected to the nerve- 

 messages. If the scheme of transmission of these mes- 

 sages through the external world is not deterministic 

 then the scheme of inference as to their source cannot 

 be deterministic, and our epistemology has been based 

 on an impossible ideal. In that case our attitude to the 

 whole scheme of natural knowledge must be profoundly 

 modified. 



These reasons will be considered at length, but it is 

 convenient to state here our answers to them in equally 

 summary form. 



(1) In recent times some of the greatest triumphs of 

 physical prediction have been furnished by admittedly 

 statistical laws which do not rest on a basis of causality. 

 Moreover the great laws hitherto accepted as causal 

 appear on minuter examination to be of statistical 

 character. 



